North Korea is a country in isolation, a place where most citizens don’t have access to the Internet or the means to travel abroad. In 2010, the New York Times described the country as a ” ‘hermit kingdom,’ so poor that there is almost no supply of concrete, bricks or window glass. People suffer shortages of rice, gasoline and even underwear.”

And yet. It’s been able to expand its weapons technology at an astounding rate. Earlier this week, it test-launched an intercontinental ballistic missile that experts say could have reached Alaska. How has the North been able to make big weaponry advances that experts considered a couple of years away at best?

The answer: North Korea has been developing its nuclear weapon systems expertise for decades. It boasts a cadre of well-trained scientists and engineers and a vast international financial network that’s both supplied the necessary raw materials and funded a billion-dollar weapons development program. And it doesn’t hurt that Kim Jong Un has made the nuclear weapons program a top priority, orienting his entire country toward that goal.

“When you have a strategic line, a single-minded focus on nuclear and economic development, and you’re able to politically mobilize and entire state infrastructure to that end, it provides a lot of potential momentum,” said Scott A. Snyder, a North Korea expert and a senior fellow at the Council on Foreign Relations. “That’s what Kim Jong Un has done.”

When North Korea first launched its missile development program, its strategy was to buy old Soviet missiles from third parties such as Egypt and Syria, said John Schilling, a North Korea expert and aerospace engineer who contributes to 38 North, a website devoted to events concerning North Korea. Once the North Korean engineers had the old missiles, they reverse-engineered them so that they could produce their own copies.

The country imported experience too, Schilling says. As the Soviet Union neared collapse, North Korea hired Russian engineers who weren’t being paid at home. It brought them to Pyongyang to both work directly on North Korean programs and train North Koreans.

North Korea also had relationships with Iran and Pakistan, Schilling said. “Initially, these seem to have been one-way affairs — North Korea sold Iran missiles to use in their war with Iraq, and Pakistan (or at least A.Q. Khan) sold nuclear technology to North Korea,” he wrote in an email. “But as all three nations developed their skills, this turned into more of an equal partnership with information and technology flowing between all three nations.” (Abdul Qadeer Khan is the founder of Pakistan’s uranium-enrichment program and has been accused of aiding the proliferation of nuclear weapons in other countries. )

At first, these efforts led to some trial and a lot of error. Not so anymore. Today, the regime is “much more efficient and effective” at producing weapons in-house, said Ken Gause, a North Korea expert at the Center for Naval Analyses. “They’re not making the same mistakes over and over again.”

Indeed, Schilling said that North Korea is mostly able to build its rockets in-house. “They do still need to import some specialized parts and components, particularly electronics, but this is done mostly on a black- or grey-market basis,” he wrote. And it’s not hard. “It doesn’t need to be done on a large scale, and it doesn’t need anyone else’s active collaboration, so it would be very difficult to stop,” he said.

The country’s speedy weapons development in the past few years, Snyder said, can be attributed to Kim.

Kim Jong Il, Kim’s father, initially developed the nuclear weapons program. But it wasn’t an overriding priority, Snyder says, and it moved at a “plodding pace.” When the younger Kim assumed power, Snyder said he “stepped on the gas pedal,” making missile development his top priority. That’s in part a political calculation — Kim was young when he took over the country, and untested. The program was a source of domestic legitimization. It also helped Kim counter the perception that North Korea is vulnerable internationally, a weak state surrounded by strong states.

Kim sees an ability to strike with nuclear weapons as the key to his legitimacy. All of which makes slowing the program down at this point a nearly impossible aim. “If North Korea wants a nuclear program, North Korea is gonna get one,” Gause said. “And we’re gonna have to live with it.”

Of course, there are still some hurdles the country needs to overcome.

Right now, its strongest warhead can detonate at about 20 kilotons, similar to the bomb dropped on Nagasaki. Reaching the abilities of an American missile warhead (which yield 100 to 475 kilotons) will require “fundamentally new designs,” Schilling said. That’s still a couple of years away, he predicts.

The country has also so far failed to show that it can fit a nuclear warhead into a missile. But that doesn’t bring Schilling much comfort.

“Every nation with North Korea’s level of demonstrated expertise in nuclear weapons development has at least been able to fit their low-yield nuclear warheads into missiles,” he wrote. North Korea has published mock-ups of how it would do it, and Schilling calls them “plausible.” He also notes that very few countries have actually demonstrated that their missiles and warheads work together.

Even the United States and Russia have done it only a handful of times. “Mostly, nations test their missiles and warheads separately and trust that they will work when brought together,” he wrote. “If the North Koreans felt compelled to put one of their warheads on one of their missiles and fire it tomorrow, odds are it would work.”

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